The consumption of high levels of triglyceride lipids has been associated with a number of health problems. Currently, obesity is one of the more prevalent metabolic problems among the general population. This condition in many people is attributed to the ingestion of a greater number of calories than is actually needed to supply energy for the maintenance and functioning of the body. Lipids are the most concentrated form of energy in the diet, with each gram of a triglyceride contributing about nine calories.
Maintaining a strict low fat diet, however, is difficult due to the fact that most people prefer the taste of "rich" foods, that is, foods that have the satisfying mouthfeel associated with fats and oils. In order for a reduced calorie food composition to adequately replace a conventional foodstuff, the fat substitute used in its preparation must mimic as closely as possible the organoleptic qualities of a triglyceride. The fat substitute must additionally have physical properties (viscosity, melting point, heat stability, thermal conductivity, etc.) resembling those of natural lipids since such properties often play a key role during preparation of a food composition. For example, in deep fat frying the oil acts as a heat transfer medium so as to impart crispness to the food being fried. At the same time, the ideal fat substitute should be non-toxic and should not cause any undesirable gastrointestinal side effects such as anal oil leakage, gas formation or diarrhea. This combination of attributes has in practice been quite difficult to achieve; the need to develop completely acceptable reduced calorie fat substitutes thus still exists.
U.S. Pat. No. 4,980,191 (Christensen) describes digestively hydrolyzable low calorie edible oil substitutes. The substitutes are esterified forms of polymerized C.sub.18 unsaturated fatty acids that have the property of being at least partially hydrolyzed during digestion into simple alcohols and polybasic acids. Although the polybasic acids generated during digestion are higher in viscosity than the corresponding esters prior to hydrolysis, thus helping to avoid a laxative effect, these fat substitutes are not ideal since the alcohol portion does contribute calories to the diet. Moreover, the liberated alcohol may have other undesirable effects. For example, where ethyl esters are employed, as in the preferred embodiment of the described substitutes, the ethanol produced will act as an intoxicant. Other types of esters, such as methyl esters, may generate toxic alcohols when ingested.
U.S. Pat. No. 5,219,604 (Klemann et al.) teaches the use in fat substitutes of inter- and intramolecular ester bridges of the formula --O--CO)(CH.sub.2).sub.n (CO--O-- where n is 1 to 8 formed by reacting dibasic acids with hydroxyl groups on the fatty side chains of fat compounds. Such fat substitutes, through the incorporation of hydroxy acids, thus inherently contain multiple ester linkages capable of being hydrolyzed upon ingestion. Where such hydrolysis takes place, the resulting hydrozylates are susceptible to further digestion; such fat substitutes may therefore have a higher level of available calories than otherwise would be desirable. Moreover, hydroxy fatty acids have certain deleterious physiological effects. The use of hydroxy fatty acids to prepare a fat substitute thus may not be desirable if digestion of the fat substitute will release such substances in the digestive tract.
U.S. Pat. No. 5,137,743 (Zaks et al.) describes the preparation of texturized oils and oil-continuous emulsions by combining liquid oils with minor amounts of certain high molecular weight polyester polymers. The polyester polymers include members of the class of polymers generally known as "alkyd" polymers, which are obtained by reaction of a polyhydric alcohol such as glycerol, a polybasic acid, and a fatty acid or oil. There is no suggestion, however, that the polyester polymers (which in the examples provided are in the form of powders) could be used by themselves at high levels as difficult to digest fat replacements in the preparation of reduced calorie food products.